SiC crystals with an optimal orientation of lattice planes for fissure reduction and method of producing same

Abstract

The present invention provides monocrystalline 4H—SiC semi-finished products having a specific orientation of its crystal structure which is set such as to reduce or even eliminate the occurrence of cracks or fissures during mechanical processing, and method of producing same. The monocrystalline 4H—SiC semi-finished product, which has a longitudinal axis and an at least partially curved lateral surface parallel to said longitudinal axis, is characterized in that the crystal structure of the 4H—SiC semi-finished product is oriented with respect to the longitudinal axis such that at each position on the lateral surface of the semi-finished product there is a line segment which is intersected by at least a predetermined minimum number of parallel cleavage planes of the {10 1 0} form per unit length, wherein the line segment is defined by a plane tangent to the lateral surface at said position.

The invention claimed is: 
     
       1. A monocrystalline 4H—SiC semi-finished product of improved mechanical robustness against cleavage, the 4H—SiC semi-finished product having a longitudinal axis and a at least partially curved lateral surface parallel to said longitudinal axis,
 characterized in that 
 the crystal structure of the 4H—SiC semi-finished product has a predetermined orientation with respect to the longitudinal axis such that at each position on the lateral surface of the semi-finished product there is a line segment which is intersected by at least a predetermined minimum number of 1000 parallel cleavage planes of the 55 10 1 0} form per millimeter of line segment length irrespectively of a position of the line segment along an outer perimeter of the 4H—SiC semi-finished product, 
 wherein the number of parallel cleavage planes ( 11 00) intersecting the line segment is less than 10000 parallel cleavage planes per millimeter of the line segment length, 
 wherein said line segment is parallel to the longitudinal axis, and 
 wherein at said predetermined orientation:
 a principal axis of the basal plane of the 4H—SiC crystal structure is tilted in the [ 11 20] direction by a first tilt angle in relation to the longitudinal axis; and/or 
 a principal axis of the basal plane of the 4H—SiC crystal structure is tilted in the [1 1 00] direction by a second tilt angle in relation to the longitudinal axis, wherein said second tilt angle is estimated based on a distance between said parallel cleavage planes of the {10 1 0} form such as to yield said at least predetermined minimum number of 1000 parallel cleavage planes of the {10 1 0} form per millimeter of the line segment length, and/or 
 the second tilt angle is a value selected from the interval [0.015°; 0.153º]. 
 
 
     
     
       2. The monocrystalline 4H—SiC semi-finished product of  claim 1 ,
 wherein 
 the form {10 1 0} parallel cleavage planes includes the cleavage planes (10 1 0), (1 1 00), and (0 1 10); and 
 said longitudinal axis is an axis of symmetry of a cylinder defined by a curved part of the at least partially curved lateral surface of the 4H—SiC semi-finished product. 
 
     
     
       3. The monocrystalline 4H—SiC semi-finished product of  claim 1 ,
 wherein 
 the first tilt angle is 4°, with a tolerance of ±0.5. 
 
     
     
       4. The monocrystalline 4H—SiC semi-finished product of  claim 1 , further comprising first and second front faces;
 wherein one or both of the first and second front faces are perpendicular to the longitudinal axis; or 
 wherein the first front face is perpendicular to the longitudinal axis and the second front face is oriented in such a way that measurements along the [1 1 00] direction yield a total thickness variation between 40 μm and 340 μm of said second front face with respect to the first front face. 
 
     
     
       5. The monocrystalline 4H—SiC semi-finished product of  claim 1 ,
 wherein: 
 said at least partially curved lateral surface has a curved part that defines a cylindrical surface with said longitudinal axis as its symmetry axis, 
 wherein said cylindrical surface has an outer diameter that substantially corresponds to a given diameter of substrate wafers obtainable by slicing the 4H—SiC semi-finished product, and/or 
 said cylindrical surface has an outer diameter of 150.0 mm±0.5 mm, 200.0 mm±0.5 mm, or 250.0 mm±0.5 mm; and/or 
 the monocrystalline 4H—SiC semi-finished product has a height larger than 15 mm, and/or 
 the monocrystalline 4H—SiC semi-finished product has a nitrogen doping larger than 1×10 18  cm −3 , and/or 
 the monocrystalline 4H—SiC semi-finished product has an orientation flat with a length of 47.5 mm±1.0 mm or a notch. 
 
     
     
       6. A method of producing a monocrystalline 4H—SiC semi-finished product with improved mechanical robustness against cleavage, the monocrystalline 4H—SiC semi-finished product having a longitudinal axis and a at least partially curved lateral surface that is parallel to said longitudinal axis, the method comprising:
 performing a process of setting a predetermined orientation of the 4H—SiC crystal structure with respect to said longitudinal axis such that at each position on the lateral surface of the 4H—SiC semi-finished product there is a line segment which is intersected by at least a predetermined minimum number of 1000 parallel cleavage planes of the 55 10 1 0} form per millimeter of length, of said line segment, irrespectively of a position of the line segment along an outer perimeter of the 4H—SiC semi-finished product, 
 wherein the number of parallel cleavage planes (1 1 00) intersecting the line segment is less than 10000 parallel cleavage planes per millimeter of the line segment length; 
 wherein said line segment is parallel to the longitudinal axis; and 
 the method further comprising: 
 estimating said predetermined orientation such as to yield the at least predetermined minimum number of 1000 parallel cleavage planes of the {10 1 0} form per millimeter of length, of said line segment. 
 
     
     
       7. The method of  claim 6 , wherein
 the form 55 10 1 0} parallel cleavage planes comprises the (10 1 0), (1 1 00), and (0 1 10) cleavage planes. 
 
     
     
       8. The method of  claim 6 , wherein the process of setting said predetermined orientation of the 4H—SiC crystal structure with respect to said longitudinal axis of the 4H—SiC semi-finished product includes:
 spatially orienting a 4H—SiC monocrystal with respect to an alignment axis such that the orientation of the 4H—SiC crystal structure is set to a predetermined tilting, in direction and amount, of the [0001]-axis of the basal plane in the 4H—SiC crystal structure in relation to said alignment axis; and 
 machining an external surface of the spatially oriented 4H—SiC monocrystal with reference to said alignment axis to form at least one of:
 a at least partially curved lateral surface that is substantially parallel to said alignment axis, and 
 at least one front face surface that is substantially orthogonal to said alignment axis; 
 
 wherein the longitudinal axis of the 4H—SiC semi-finished product corresponds to the alignment axis of the spatially oriented 4H—SiC monocrystal. 
 
     
     
       9. The method of  claim 8 , wherein
 the process of setting the predetermined orientation of the 4H—SiC crystal structure is performed on a raw 4H—SiC monocrystal and includes performing angle measurements of the 4H—SiC crystal structure to determine the orientation of the principal axis of the basal plane, and 
 wherein the 4H—SiC semi-finished product is obtained, after the process of setting is completed on the raw 4H—SiC monocrystal, by performing the following steps:
 machining at least one front face surface along said initial orientation, and 
 machining the at least partially curved surface in a direction transverse to said initial direction. 
 
 
     
     
       10. The method of  claim 6 , wherein the process of setting said
 predetermined orientation of the 4H—SiC crystal structure includes: 
 orienting the basal plane of the 4H—SiC crystal structure with an initial orientation; 
 tilting the basal plane from the initial orientation to a first orientation by a first tilt angle in the [ 11 20] direction of the 4H—SiC crystal structure; and 
 tilting the basal plane from the first orientation to a second orientation by a second tilt angle in either the 8 1 1 00] direction or the [ 1 100] direction of the 4H—SiC crystal structure; 
 wherein in said initial orientation the basal plane is substantially perpendicular to the longitudinal axis of the final oriented 4H—SiC semi-finished product. 
 
     
     
       11. The method of  claim 10 , wherein
 the first tilt angle is 4°, with a tolerance of ±0.5°; and/or 
 wherein said second tilt angle is estimated based on a distance between said parallel cleavage planes of the {10 1 0} form such as to yield said at least predetermined minimum number of 1000 parallel cleavage planes of the {10 1 0} form per millimeter of line segment length that intersect the line segment, and/or 
 the second tilt angle is a value selected from the interval [0.015°; 0.153°]. 
 
     
     
       12. The method of  claim 6 , wherein the process of setting the
 predetermined orientation of the 4H—SiC crystal structure includes: 
 orienting the basal plane of the 4H—SiC crystal structure with an initial orientation; 
 rotating the basal plane about said initial orientation by a predetermined rotation angle in a clockwise direction; 
 tilting the rotated basal plane by a third tilt angle in the [ 11 20] direction of the 4H—SiC crystal structure; and 
 wherein in said initial orientation the basal plane is substantially perpendicular to the longitudinal axis of the final oriented 4H—SiC semi-finished product. 
 
     
     
       13. The method of  claim 12 , wherein
 the predetermined rotation angle is a value within the range [0.22°, 2.19°], and/or 
 the third tilt angle is 4°, with a tolerance of ±0.5°. 
 
     
     
       14. The method of  claim 6 , wherein the process of setting the
 predetermined orientation of the 4H—SiC crystal structure includes: 
 orienting the basal plane of the 4H—SiC crystal structure with an initial orientation; 
 rotating the basal plane about said initial orientation by a predetermined rotation angle in a counter-clockwise direction; 
 tilting the rotated basal plane by a third tilt angle in the [ 11 20] direction of the 4H—SiC crystal structure; and 
 wherein in said initial orientation the basal plane is substantially perpendicular to the longitudinal axis of the final oriented 4H—SiC semi-finished product.